High temperature inorganic gel grease compositions



United States Patent HIGH TEMPERATURE INDRGANIC' GEL GREASE COMPOSITIONSWalter H. Peterson, Point Richmond, and Stanley T. Abrams and Fred H.Stress, Berkeley, Calif., assignors to Shell Development Company, NewYork, N. Y., a corporation of Delaware No Drawing. Application August29, 1955 SerialNo. 531,266

7 Claims. (Cl. 252-28) This invention relates to improved greasecompositions. More, particularly, it is concerned with greasesexhibiting exceptionally high stability at elevated temperatures.

Grease compositions ordinarily comprise a liquid medium and a gellingagent therefor. The liquid medium is preferably one possessinglubricating properties and the gelling agent is ordinarily a soap or acolloidal material of inorganic origin. Mineral lubricating oils areprimarily useful as the lubricating medium and soaps, such as those offatty acids or hydroxy fatty acids, are. com* monlyemployed as gellingagent.

The present invention is directed to grease compositions containinggelling agents of inorganic origin as one of the essential constituents.Greases have been prepared heretofore which utilize amorphous colloidalgels, such as silica and the like, or which employ clays or onium claysas the grease-forming material. The latter clays comprise highbase-exchange clays which have been converted to oleophilic materials bybase exchange with oleophilic onium compounds such as quaternaryammonium materials or their phosphonium, sulfoniurn or stiboniumanalogs.

Greases gelled with. ordinary soaps are useful for operation underrelatively mild temperature conditions but at elevated temperatures, inthe order of 200 F. or higher, soap greases rapidly soften andeventually be come fluid. This is apparently due to phase changes whichoccur in the soap fibers as they change from one crystal form toanother. Greases gelled with colloids of inorganic origin exhibit theadvantage of maintaining their consistency over a far Wider temperaturerange. Due to their inorganic character, the gels do not pass throughphase changes at temperatures below about 500 C.- but maintain theoriginal structure of the grease substantially in its original state.Hence, the limiting character of such greases is not the softeningthereof but instead is dependent upon the thermal and oxidationstability and volatility of the liquid component of the grease.

High temperature greases containing gelling agents of inorganic originmay utilize either mineral oil lubricants or synthetic fluids as theliquid phase. Since volatility is one of the limiting characteristics,any greases to be employed at high temperature must, of course, containa major amount of high boiling oleaginous fluid.

Greases to be used at elevated temperatures for many purposes must be ofrelatively low cost if they are to be economically practical. Hence, itis highly desirable to employ a petroleum oil fraction as a major orsole component of lubricating oil phase of high temperature greases, butlubricating oils exhibit rapidly increasing decomposition when subjectedto heat and oxidation influences. The addition of ordinaryanti-oxidants, such as alkyl phenols or aromaticamines, has been foundto be substantially ineffective above about 300 F. In fact, the courseof oxidation at such elevated temperatures appears to be actuallyaccelerated by these materials rather than j'etarded.

It. is an object of the present invention to provide grease compositionsuseful at high temperatures. It is another object of this invention toprovide grease compositions which: maintain their structure andstability at elevated temperatures. It is a further object of thisinvention to provide grease compositions utilizing mineral oil fractionsas a major component of the lubricating oil phase but which are stablewhen employed at high temperatures. Other objects will become apparentduring the following description.

Now, in accordance with this invention, it has been found that greasesgelled with a thickener of the group consisting of silica-containing.inorganic amorphous colloids, clays and onium clays can be maderemarkably stable to decomposition at elevated temperatures (even. at ashigh as 300-450 F.) by the combination of from about 1% to about 25% byweight, based. on the total grease, of carbocyclic hydrocarbons havingmolecular weights within the range of from. about 300 to about 750, andfrom about 0.5% to about 20% by weight, based on the. total composition,of a basic inorganic zinc compound, such as zinc oxide, zinc hydroxide,zinc borate and zinc carbonate, the balance of the compositioncomprisinga majorproportion of a lubricating oil.

The zinc compounds are preferably utilized in amounts between about 2.5%and about 10% by Weight of the total grease. They should be utilized inthe form of finely divided particles, such as utilized for paintpigments or the like, and preferably have particle sizes less than about1.0 microns. Such finely divided powders can be easily incorporated ingreases by milling or other shearing means, or may be. formed in situ.

The carbocyclic hydrocarbons may be monocyclic or polycyclic, have.molecular weights between about 300 and about 750, and preferablycomprise higher aromatics or naphthenes. Typical donors are as follows:

Z-methylnaphthalene 2,6-dimethylnaphthalene 2,3-dimethylnaphthalenen-Propylcyclohexane Cis-1,3-dimethylcyclohexane Trans-1,4-dimethylcycloh exane cyclohexene l-methyl cyclohexene n-tetrahydrophthalic acid A -cyclohexadiene A cycloh exadiene A-dihydronaphthalene n -dihydronaphthalene n -dihydronaphthaleneIsopropylcyclohexane Amylcyclohexane Triethylcyclohexane Cis-decalinTrans-decalin Hexahydroindane Cyclopentylcyclohexane BicyclohexylAmyldecalin Abietanes The proportion of carbocyclic hydrocarbonmaterial.

required for effective stabilization of the present compositions isrelatively insignificant but should be. at least about 1% by weight ofthe final grease composition. The carbocyclic hydrocarbons may be alubricant per se or may be added together with other lubricatingcomponents. Preferably the carbocyclic hydrocarbon is pres- 3 ent in anamount between of the grease composition. In most cases the carbocyclichydrocarbon comprises more than one of the above types of compounds, butthe use of single carbocyclic hydrocarbons is also contemplated.Cycloaliphatic (naphthenes) are preferred and especially those havingmolecular weights in the range of 300-750. In the case of certainlubricating oil fractions, such as bright stock, cylinder stock, and thelike, the naphthenes may occur naturally, but in other instances, suchas in synthetic lubricating materials, it may be necessary to add them.In the latter case, the naphthenes present in bright stock are suitablesubstances.

One aspect of the present invention comprises the process of operatingand utilizing grease compositions at temperatures above about 300 F. inthe presence of the above-described carbocyclic hydrocarbons and basicinorganic zinc compounds, whereby substantial protection againstoxidative and thermal decomposition of the grease is accomplished. Theseessential zinc compounds and carbocyclic hydrocarbons may be combinedwith standard organic oxidation inhibitors so that the resultingcompositions are not only protected against oxidation at temperaturesabove about 300 F., but also at lower temperatures encountered duringoperation. Thus, the present compositions may be modified by thepresence of polynuclear aromatic amines such as phenyl-a-naphthylamineor by the addition of phenolic inhibitors such as 1,2-dihydroxybenzeneand alkylated phenols.

Another desirable type of oxidation inhibitor to be included comprisesone or more epoxy compounds and particularly glycidyl substances, suchas glycidyl phenyl ether. Still further protection against degradationat elevated temperatures may be obtained by the inclusion at thesetemperatures of metallic sulfides, such as zinc sulfide, copper sulfide,tungsten sulfide, and the like. The latter type of materials appears tooperate by coating the metallic surfaces with which the grease comes incontact, thereby masking the metal as a possible oxidation catalyst.

The major gelling agent in the subject greases is a colloid of inorganicorigin, including silica-containing amorphous colloids, clays and oniumclays utilized in amounts sufiicient to gel the oil to a greasestructure, normally in proportions of l-15 by weight of the totalgrease. For the most part, such gelling agents include silica.Improvements in corrosion characteristics of the subject greases areobtained by combinations of silica with a minor proportion of analkaline earth metal oxide such as magnesia or lime. It is believed thatthe mixed gelling agents chiefly comprise a mixture of silica with thealkaline earth metal oxide although some alkaline earth metal silicatemay be present as well. Onium clays are prepared by dispersing highbase-exchange clays, such as Wyoming bentonite, or hectorite, in waterand adding thereto a quaternary onium compound such as dimethyldioctadecyl ammonium bromide. The base exchange which occurs results inthe formation of the so-called onium clay which preferably bears atleast 50 milliequivalents of an onium radical per 100 grams of clay.Such onium clays are capable of swelling at least ten times theiroriginal dry volume in nitrobenzene. For this purpose the onium compoundshould bear at least one hydrophobic radical longer than 15 Angstromsand preferably having an area greater than 70 square Angstroms. For thispurpose at least one of the organic radicals should contain more thanabout carbon atoms in a straight chain. Other suitable onium compounds,which may be used in the formation of onium clays, include dodecylammonium acetate, triphenyl lauryl phosphonium bromide, didodecylethylsulfonium bromide, decyltriphenyl arsonium bromide, as Well as theiranalogs and homologs.

The amorphous gelling agents are preferably incorporated in thelubricating oil while in a highly expanded 5% and 25% of the weight 7 4state of subdivision- The density of the amorphous gelling agents, suchas silica and the like, should be between about 0.01 and 0.2 gram permilliliter such as can be obtained by the aerogel technique. Accordingto the latter process, silica gel is dehydrated by solvent displacementwith a low boiling liquid such as acetone or alcohol. The organogel soprepared is heated in an autoclave, or other pressure equipment, abovethe critical temperature of the solvent at which point the pressure isreleased and the solvent flashed oif, leaving the silica or similar gelin a highly expanded form particularly useful for the formation ofgrease structures with lubricating oils. Other processes which may beemployed to create similar substances substantially equivalent orsuperior to aerogels include the solvent transfer process wherein theorganogel referred to above is added to a mineral lubricating oil, afterwhich the more volatile liquid is removed by distillation. The oleogelwhich remains may then be milled into a grease structure. A stillfurther process comprises admixture of the hydrogel of silica or thelike with a hydrophobic surface-active agent, such as a high molecularweight amine or partial amide, filtration of a major proportion of theWater which thereupon separates, incorporation of the concentratedmodified hydrogel with mineral oil and subse quent removal bydistillation or settling of water from the resulting mixture. The latterprocess is preferred due to its economy and convenience. Moreover, thepresence of the hydrophobic surface-active agent provides the greasewith waterproofed properties which it would .not otherwise possess.

. While it is possible to improve the oleophilic character of thegelling agents described herein by chemical reaction between baseexchanging gelling agents such as clay and onium compounds, this is notessential. If a hydrophobic or oleophilic grease composition is desired,

it is merely necessary to absorb on the surface of the gelling agents(amorphous colloids or clays) a hydrophobing proportion of a catonichydrophobic surfaceactive agent. are described in such 2,623,852 and U.S. 2,623,853.

The lubricating oil to be employed in the subjectgreases may be ofeither natural or synthetic origin.

Mineral oils particularly useful are preferably residual oils commonlyknown as cylinder stocks or bright stocks.'

While the present invention is not to be confined to the use of amineral oil derived from any particular source or by any particularrefining process, the usual source of suitable mineral oils comprisesthe fraction thereof generally termed bright stocks, and particularlybright stocks having a viscosity index of 60105. The term bright stockis one which is well recognized and commonly. used in the art ofrefining mineral oils. To obtain the desired fraction, suitablelubricating stock crude oils are usually subjected to distillation underordinary atmospheric or slightly reduced pressures in order to obtain along residue comprising the fraction which does not distill under theseconditions without substantial decomposition. The long residue is thensubjected to vacuum distillation, often inthe presence of steam. Underthese conditions, gas oil and distillate lubricant fractions distillover, leaving what is normally termed a short residue or a steam refinedstock, also known as cylinder stock. The steam refined stock is thendeasphalted (if an asphaltic crude is employed) and subjected todewaxing operations to remove microcrystalline or macrocrystallinewaxes. Following this, the dewaxed oil is treated with a solvent for thepurpose of removing at least a portion of the aromatic components,except for a very highly parafiinic oil. percolation may be employed toclean up the oil following any one or all of these separate operations.The raffinate which remains after deasphalting, dewaxing, extraction,andclay treatment is generally called bright stock? The amounts andidentities of these agents patents as U. S. 2,554,222, U. S.

Clay contact treatment or The bright stocks for use in the presentcompositions should have the ranges of properties given in Table I:

TABLE I Properties of bright stocks Tables 11 and III give theproperties of typical bright stocks which are useful in the compositionsof this invention:

properties, the other properties such as flash, fire, aniline point, andviscosity index usually are largely dependent upon them. In addition tothe bright stocks and the like described above, synthetic lubricants canbe utilized, including especially the ester type of lubricant andaliphatic polyethers. Representative classes of esters which may beemployed are carboxylates, phosphates, and silicates. Polyetherscomprise polyalkylene oxides and polyalkylene glyocols which may haveeither or both ester or ether end groups. All of these classes ofmaterials have been fully described in the lubricating oil art. For thepresent high temperature greases species should be selected showing asuitable viscosity at the temperature contemplated during the use of thegrease. Preferably they should exhibit an evaporation rate of less thanabout 5% at 400 F. in 8 hours.

Suitable species include bis(2-ethylhexyl)sebacate, and thecorresponding dialkyl esters of dicarboxylic acids, said acids havingfrom 4 to 16 carbon atoms separating the carboxyl groups and the alcoholportion of said TABLE II Examples of typical bright stocks SUS RingAnalysis Ratio of Aver. Viscosity Paraflins Aver. Rings Index to Naph-Mol per 100 210 Aro- Naph- Parafiins thenes Wt. Mol

matic thenes Mid Continent Bright Stock, Conventional Extraction 3, 650164 77 13 17 70 4.1 685 3.7 Mid Continent Bright Stock, Mild Extraction2, 569 141 85 9 19 72 3.8 685 3.4 Mid Continent Bright Stock, HeavyExtraction 2, 049 131 03 3 21 76 3.62 675 2.9 Pennsylvania Bright St0ckr 2,10 144 102 5 16 79 4. 95 730 3. 0 Gulf Coastal Bright Stock 1, 25185 63 4-. 61 1. 74 515 3.4

TABLE III Specifications for typical Mid-Continent bright stocksUnfiltered Filtered 25. 5 24.5 25. 5 8+ Dark Green. 6. 7 10 10 10 540580 545 k 90 so It will be understood from the above analyses that thesource or treatment of a particular mineral oil is not as important forthe present purpose as the final properties of the mineral oil to beused in these compositions. For example, it is possible to vary theextent of solvent extraction dependent upon the original aromaticcontent and the requirements of the specific use of the final product,as Well as upon the necessity or desirability of deasphalting, claytreating, acid treating, and the like. Hence, it will berecognized thatthe present invention is predicated upon the use of a mineral oilfraction having the abovedefined ranges of properties and not upon thesource or treatment of such oil.

In addition to their naphthenes, the two most important inherentproperties of a mineral oil suitable for the present use comprise thearomatic content and the viscosity characteristics. The aromatic contenthas a large influence upon the sensitivity of the oil to thermal changesand the viscosity of the oils defines their suitability for theirpresent purposes. Hence, the best definition with respect to essentialcharacteristics of mineral oils suitable for the present compositionscomprises those having an aromatic hydrocarbon content less than about15% by weight and having a viscosity of between about 1250 and about11,000 SUS at 100 F. Having defined these particular esters beingderived from monoor poly'hydric alcohols containing at least about 4carbon atoms, and preferably from 6 to 12 carbon atoms each. Phosphorusacid esters which may be employed include not only organic phosphates,but also phosphonates and phosphinates; corresponding phosphine oxidesare also suitable. Phosphorous esters which have been found to beespecially suitable include tricresyl phosphate, trioctyl phosphate,diphenyl cresyl phosphate, diphenyl o-ctyl phosphate, dinonylisooctenephosphonate, bis(phosphonoethyl)ether, and the like. Suitablesilicon esters include the trialkyl silicates wherein each alkyl grouphas from 2 to 8 carbon atoms, such as tetrabutyl silicate andtetra-Z-ethylhexyl silicate. The corresponding thiasilicates [e. g.tetra(7-methyl-4-thiaoctyl)silicate] are also useful and impart extremepressure properties to the greases containing them. Alyklene oxidepolymers may be prepared by known processes of polymerizing alkyleneoxides or glycols such as propylene oxide or ethylene oxide or ofcopolymerizing ethylene oxide with propylene oxide. The resultingmixture of polymeric materials preferably has a molecular weight betweenabout 200 and 2000, and contains polyoxyalkylene chains terminating inhydroxyl radicals. These may be modified by esterification oretherification for the preparation of polymeric derivatives havingimproved lubricating properties. Particularly desirable types includethose in which at least about 25% by weight of the end groups areetherified with alcohols which have from 4 to 12 carbon atoms permolecule and wherein at least 25 of the terminal hydroxyls areesterified with aliphatic carboxylic acids having between 2 and 20carbon atoms per molecule.

In demonstrating the effectiveness of the subject earbocyclichydrocarbons combined with the Zinc iconipounds for reducing the thermaland oxidative decomposition tendencies of greases, three types of testswere employed: In the first test, a film of the grease compositionapproximately 0.013 inch in thickness is spread on a sanded steel plateand heated for 6 hours at 400 F. in an atmosphere of circulating air. Agrease consisting of 90% by weight of Mid-Continent bright stockcontaining 16% by weight of naphthenic hydrocarbons and silica aerogelin an amount of by weight of the grease oxidizes to a hard lacquer underthese conditions.

When the same grease is modified with 10% by weight of zincoxide, andheated under the same conditions, the grease film remains plastic andappears to be substantially unchanged from its condition at the start ofthe test. 7

Modification of the original silica-bright stock grease with 10% byweight thereof of zinc carbonate gives substantially the same degree ofstabilization as obtained by the use of zinc oxide. In order to showthat this phenomenon is not of wider applicability, a correspondingtest, made with the same silica-bright stock grease modified by thepresence of 10% by Weight thereof of alumina, results in a grease filmafter the test period which is a very hard varnish having no grease-likeproperties remaining.

Parallel tests were made upon grease compositions comprising 92% byweight of the same bright stock lubricating oil gelled with 8% by weightof a dimethyl dioctadecyl ammonium clay, said ammonium clay hav ing thetrade name Bentone 34. In the absence of any further modification, thefilm of grease after the test period is an extremely hard varnish. Theaddition of 10% by weight of zinc oxide to this grease before the testperiod results in a grease film upon testing which is stiffened somewhatbut is not the hard varnish obtained by the unstabilized composition.The substitution of 10% zinc carbonate in place of zinc oxide results ina grease which remains plastic and is easily worked even after the testperiod. However, the substitution of 10% by weight of alumina for thezinc compound provides no stabilization of the ammonium clay-brightstock grease, the heat tested grease film being very hard.

A second test comprises heating a diluted grease composition in a Dornteoxidation apparatus at 180 C. to determine the rate of oxygen absorptionin the presence an iron catalyst. For this purpose the greases arediluted with additional quantities of the same mineral lubricating oilemployed in the original grease in order to provide a fluid enoughstructure for oxygen to bubble therethrough. Under the conditionsdescribed a fluid grease comprising 2% silica and a mineral oil brightstock requires only 1.1 hours to absorb 1500 cc. of oxygen. A similarcomposition modified by the presence of 10% zinc carbonate is stable forapproximately six times the period in which the uninhibited compositionwas tested.

A third test for investigating the elfect of the present compositionscomprises utilizing the grease in a bearing rig operated at 400 F. tolubrication failure involving a high level or stalling of the rig. Inthis test the rig is operated for four hours at ambient temperature andthen raised to the operating temperature of 400 F. for ten hours. Themachine is then stopped for ten hours and the cycle then repeated. Underthese conditions a silicabright stock grease containing 10% silica geland 90% bright stock lasts for only about four to six cycles. Theaddition of 10% zinc carbonate causes a 200 to 300% increase in cyclelife.

This application is a continuation-in-part of application Serial No.299,016, filed July 15, 1952, now abandoned, said application being acontinuation-in-part of application Serial No. 170,248, filed June 24,1950, now U. S. Patent 2,658,869.

We claim as our invention:

1. A grease composition consisting essentially of a major amount of amineral lubricating oil containing 1 to by weight, based on the totalgrease, of carbocyclic hydrocarbons having molecular weights within therange of from about 300 to about 750, a greaseforming proportion of agrease-forming gel of the group consisting of amorphous inorganiccolloids predominating in silica, hectorite and bentonite clays havingadsorbed on the surface thereof a hydrophobing proportion of a cationichydrophobic surface active agent, and onium hectorite and bentoniteclays, and between about 0.5% and about 20% by weight of a compoundselected from the group consisting of zinc oxide, zinc hydroxide, zincborate and zinc carbonate.

2. A grease composition consisting essentially of a major amount of amineral oil bright stock having a viscosity between about 1250 and about11,000 SUS at F., a viscosity index of 60-105 and containing 125% byweight, based on the total grease, of naphthenic hydrocarbons havingmolecular weights within the range of from about 300 to about 750', agelling proportion of a grease-forming silica gel, and between about 0.5and about 10% by weight of zinc carbonate.

3. A grease composition consisting essentially of a major amount of amineral oil bright stock having a viscosity between about 1250 and about11,000 SUS at 100 F., a viscosity index of 60-105 and containing 125% byweight, based on the total grease, of naphthenic hyrocarbons havingmolecular weights within the range of from about 300 to about 750, agelling proportion of a grease-forming dimethyldioctadecyl ammoniumbentonite clay gel, and between about 0.5% and about 10% by weight ofzinc carbonate.

4. A grease composition consisting essentially of a major amount of amineral oil bright stock having a viscosity between about 1250 and about11,000 SUS at 100 F., a viscosity index of 60-105 and containing 1-25%by weight, based on the total grease, of naphthenic hydrocarbons havingmolecular weights within the range of from about 300 to about 750, agelling proportion of a grease-forming silica gel, and between about 0.5and about 10% by weight of zinc oxide.

5. A grease composition consisting essentially of a major proportion ofa mineral lubricating oil containing 1-25% by weight, based on the totalgrease, of said oil of naphthenic hydrocarbons having molecular weightswithin the range of from about 300 to about 750, a gelling proportion ofa silica grease-forming gel, and between about 0.5 and about 10% byweight of zinc carbonate.

6. A grease composition consisting essentially of a major proportion ofa mineral lubricating oil containing 1-25% by weight, based on the totalgrease, of cycloaliphatic hydrocarbons having molecular weights withinthe range of from about 300 to about 750, a gelling proportion of agrease forming dimethyldioctadecyl ammonium bentonite clay gel havingadsorbed on the surface thereof a hydrophobing proportion of a cationichydrophobic surface-active agent, and from about 0.5 to about 10% byweight of zinc carbonate.

7. A grease composition consisting essentially of a major amount of amineral lubricating oil containing 125% by weight, based on the totalgrease, of carbocyclic hydrocarbons having molecular weights within therange of from about 300 to about 750, a grease-forming proportion of agrease-forming gel of the group consisting of amorphous inorganiccolloids predominating in silica, hectorite and bentonite clays havingadsorbed on the surface thereof a hydrophobing proportion of a cationichydrophobic surface active agent and onium hectorite and bentoniteclays, and between about 0.5 and about 20% by weight of a basicinorganic zinc compound.

References Cited in the file of this patent UNITED STATES PATENTS2,583,604 Sirianni et al Jan. 29, 1952 2,599,683 Abrams et al. June 10,1952 2,623,852 Peterson Dec. 30, 1952 2,625,508 Stross Jan. 13, 19532,681,314 Skinner et al. June 15, 1954

1. A GREASE COMPOSITION CONSISTING ESSENTIALLY OF A MAJOR AMOUNT OF AMINERAL LUBRICATING OIL CONTAINING 1 TO 25% BY WEIGHT, BASED ON THETOTAL GREASE, OF CARBOCYCLIC HYDROCARGONS HAVING MOLECULAR WEIGHTSWITHIN THE RANGE OF FROM ABOUT 300 TO ABOUT 750, A GREASE FORMINGPORPORTION OF A GREASE-FORMING GEL OF THE GROUP CONSISTING OF AMORPHOUSINORGANIC COLLORIDE PREDOMINATING IN SILICA, HECTORITE AND BENTONITECLAYS HAVING ADSORBED ON THE SURFACE THEREOF A HYDROHOBING PROPORTION OFA SATIONIC HYDROPHOBIC SURFACE ACTIVE AGENT, AND ONIUM HECTORITE ANDBENTONITE CLAYS, AND BETWEEN ABOUT 0.5% AND ABOUT 20% BY WEIGHT OF ACOMPOUND SELECTED FROM THE GROUP CONSISTING OF ZINCE OXIDE, ZINCHYDROXIDE, ZINC BORATE AND ZINC CARBONATE.